The present invention relates to the formation of thermoplastic and cross-linked polymeric networks and more particularly to improving the physical properties thereof by controlling gravitational conditions during the POLYMERIC network formation.
It is known that when a polymer is cast from a volatile solvent solution, a large temperature gradient and concentration gradient occurs within a very short time period which gradients strongly influence the type of film structure formed under these conditions. Polymer membrane structures are very sensitive to the type of polymer, the type of solvents used to dissolve and cast or quench the film structure, and the rate of evaporation used to prepare the membrane. Conventional gas separation membrane technology has been reported to be moving towards thinner and more dense film structures (even plasma polymerized film structures) having high strengths and very small (e.g., 1,000 A and below) pore size structures. The use of high pressure to create polymer structures with dense film structures and small pore sizes for enhanced separation/selectivity and membrane properties has been reported. The use of polymer membranes in application areas where the pore sizes are much larger, e.g., on the order of 5-200 .mu.m (micro filtration), depends on factors including defects, strength, permeability, selectivity, and like factors. Thin films having controlled morphology in the area of non-linear optical (NLO) opto-electronic devices is yet another area of current research endeavors in thin film or membrane processing technology.
Polymer membrane structures have been proposed for a wide variety of uses including, for example, separations (gas, liquid, or combinations), purification, enrichment, as protective layers, adhesives, and even as artificial skins. Nevertheless, approximately 60% of synthetic polymeric membranes currently are utilized as semipermeable barrier layers in the separations industry. Another polymer membrane structure receiving attention involves asymmetric polymer membranes. Such membranes are prepared by a process known as "phase inversion" and essentially involves casting of a polymer/solvent solution into a thin layer on a smooth solid surface, subjecting the solution to an evaporation step in which some of the solvent volatilizes, and a precipitation step where the polymer/solvent film is immersed into a bath of non-solvent. The resulting membrane consists of a thin dense skin layer which behaves as a semi-permeable barrier controlling the permeation and rejection properties of the membrane and a thick porous layer which provides support and structural integrity for the skin to withstand the imposed mechanical stresses. Polymer Preprints, Vol. 30, No. 1, pp 36-37 (April 1989). Further information on polymer membrane structures can be found in "Permeation of Carbon Dioxide through Homogeneous and Asymmetric Polysulfone Membranes", Journal of Polymer Science: Part B: Polymer Physics, Vol. 27, 919-927 (1989); "Perm Selective Membranes Separate Gases", Chemtech, 232-238 (April 1986); and "Membranes and Films from Polymers", Journal of Chemical Education, Vol. 63, No. 5, 414-417 (May 1986), the disclosures of which are expressly incorporated herein by reference.
Besides polymer membrane structures which may be influenced by gravity during the membrane formation, the processing of commercial polymeric materials involving the interaction of polymers with materials of different density (such as other polymers, metal particles or fibers, metal oxides, glass, carbon fibers, etc.) involve interactions of non-uniformity because of gravity-driven settling or dispersion of the different materials. To compensate for these dispersion effects, industry has developed special additives to help promote uniform interaction (e.g., by means of wetting, particle-particle repulsion, surface energy effects, etc.) among the different phases.
The foregoing polymeric network structures have physical properties which may be influenced by gravitational effects. The challenge is to apply gravity for improving the properties desired in polymer membrane structures and bulk polymer network articles.